net/tap: fix rx cksum flags on TCP packets

net/tap: fix rx cksum flags on TCP packets

Since commit d5df2ae0428a ("net: fix unneeded replacement of TCP
checksum 0"), the functions rte_ipv4_udptcp_cksum() or
rte_ipv6_udptcp_cksum() can return either 0x0000 or 0xffff when used to
verify a packet containing a valid checksum.

This new behavior broke the checksum verification in tap driver for TCP
packets: these packets are marked with PKT_RX_L4_CKSUM_BAD.

Fix this by checking the 2 possible values. A next commit will introduce
a checksum verification helper to simplify this a bit.

Fixes: d5df2ae0428a ("net: fix unneeded replacement of TCP checksum 0")
Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>